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99 lines
3.6 KiB
Python
99 lines
3.6 KiB
Python
"""Registers functions to be called if an exception or signal occurs."""
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import logging
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import os
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import signal
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import traceback
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logger = logging.getLogger(__name__)
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# _SIGNALS stores the signals that will be handled by the ErrorHandler. These
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# signals were chosen as their default handler terminates the process and could
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# potentially occur from inside Python. Signals such as SIGILL were not
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# included as they could be a sign of something devious and we should terminate
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# immediately.
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_SIGNALS = ([signal.SIGTERM] if os.name == "nt" else
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[signal.SIGTERM, signal.SIGHUP, signal.SIGQUIT,
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signal.SIGXCPU, signal.SIGXFSZ, signal.SIGPWR])
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class ErrorHandler(object):
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"""Registers functions to be called if an exception or signal occurs.
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This class allows you to register functions that will be called when
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an exception or signal is encountered. The class works best as a
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context manager. For example:
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with ErrorHandler(cleanup_func):
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do_something()
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If an exception is raised out of do_something, cleanup_func will be
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called. The exception is not caught by the ErrorHandler. Similarly,
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if a signal is encountered, cleanup_func is called followed by the
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previously registered signal handler.
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Every registered function is attempted to be run to completion
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exactly once. If a registered function raises an exception, it is
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logged and the next function is called. If a (different) handled
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signal occurs while calling a registered function, it is attempted
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to be called again by the next signal handler.
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"""
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def __init__(self, func=None):
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self.funcs = []
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self.prev_handlers = {}
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if func is not None:
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self.register(func)
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def __enter__(self):
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self.set_signal_handlers()
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def __exit__(self, exec_type, exec_value, trace):
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if exec_value is not None:
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logger.debug("Encountered exception:\n%s", "".join(
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traceback.format_exception(exec_type, exec_value, trace)))
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self.call_registered()
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self.reset_signal_handlers()
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def register(self, func):
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"""Registers func to be called if an error occurs."""
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self.funcs.append(func)
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def call_registered(self):
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"""Calls all registered functions"""
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logger.debug("Calling registered functions")
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while self.funcs:
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try:
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self.funcs[-1]()
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except Exception as error: # pylint: disable=broad-except
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logger.error("Encountered exception during recovery")
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logger.exception(error)
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self.funcs.pop()
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def set_signal_handlers(self):
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"""Sets signal handlers for signals in _SIGNALS."""
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for signum in _SIGNALS:
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prev_handler = signal.getsignal(signum)
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# If prev_handler is None, the handler was set outside of Python
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if prev_handler is not None:
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self.prev_handlers[signum] = prev_handler
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signal.signal(signum, self._signal_handler)
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def reset_signal_handlers(self):
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"""Resets signal handlers for signals in _SIGNALS."""
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for signum in self.prev_handlers:
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signal.signal(signum, self.prev_handlers[signum])
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self.prev_handlers.clear()
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def _signal_handler(self, signum, unused_frame):
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"""Calls registered functions and the previous signal handler.
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:param int signum: number of current signal
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"""
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logger.debug("Singal %s encountered", signum)
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self.call_registered()
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signal.signal(signum, self.prev_handlers[signum])
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os.kill(os.getpid(), signum)
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